Ask the fish store what they were feeding there, perhaps? I've never kept either of those fish, but I have yet to find anything that couldn't resist freeze-dried bloodworms. (I like the hikari brand). I also have sinking algae wafers for my otos and I'm not sure that they actually ever get to eat any of them, since all the other fish like them so much. (Omega One Veggie Rounds). All the tetras I've kept have seemed to like the Hikari micro pellets as well.
Just be sure you are careful to clean out any uneaten food, since you are cycling and it can give you ammonia spikes as it decomposes.
Fish are cold-blooded, so they can go a while without eating. I wouldn't panic.
How big are your shrimp pellets? Definitely small enough to fit in those tiny little mouths?
Try crumbling some flake into smaller pieces in case they've never encountered a flake before?